Plant Doctor Archive

Getting the best from rhubarb

WE have a large rhubarb plant with huge leaves but the stalks are not turning red. We've tried removing some of the outside leaves to expose the stalks to more light, but it has made no difference. The garden gets full sunlight and is sheltered.

WE have a continual problem with leaves on our rhubarb turning yellow and wilting. When living in Hamilton, our plants were lush with large juicy stalks. Apart from the odd sprinkle of fertiliser and watering, they flourished. But not so in Papamoa, where we have a very sandy soil. Even after trying several doses of potash, general fertiliser and plenty of water, the plants never produce stalks of any great size with many turning yellow and dying before reaching maturity.

RHUBARB grows best in a relatively cool climate - it can tolerate temperatures as low as minus 15°C in winter. It also needs a plentiful supply of water during the growing season and generous feeding, but good drainage is also essential.

It's quite common for the stalks not to turn red and there's not always an obvious answer as to why this happens. Some experts say lack of light, others say high temperatures while the stalk is growing, yet other factors such as high nitrogen fertilisers could also play a part. There is also a colour difference between varieties.

You can grow rhubarb in warm areas, but generally the stalks do seem to be redder on plants grown in cooler parts of the country. But once cooked, the green stalks are just as nice to eat as red ones, though less attractive on the plate.

There are a few diseases that can cause problems with rhubarb and they tend to occur most when drainage is poor or when temperature and humidity are high. Yellowing and wilting of the leaves could simply be lack of water at crucial times - the broad leaves need copious amounts of moisture in summer. Or it could be a fungal disease. Check the crown of the plant at the base of the leaves close to soil level for white fungal growth or rot. If you find any, it's best to remove the plant completely and buy a new, healthy one to plant elsewhere in the garden.

Other tips are to feed regularly in the growing season with a high potassium fertiliser and to remove any flowering stems as soon as they appear. It is also worth remembering that rhubarb can tolerate shade, so you don't have to plant it in a sunny spot.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.